A technique, commonly referred to as a cell block preparation, has been used for preparing embedded biological samples for further analysis. The cell block procedure immobilizes cells or small tissue fragments in a solid or semi-solid support, typically paraffin or wax. Thin sections of the cell block are then cut with a microtome and the sections mounted onto a microscope slide for examination. The resulting sections from the cell block display diagnostic information in a manner that complements direct deposition techniques.
The cell block preparation method requires that the cell fragments be “embedded” in a solid or semi-solid medium, most commonly paraffin wax. “Embedding” typically requires the following steps: (1) all water molecules must be removed from the cells, typically by alcohol (water is miscible with alcohol); (2) all alcohol must then be removed, as well as all fatty substances, and replaced typically by xylene (xylene is miscible with alcohol but not water); (3) the xylene must be removed and replaced with wax (wax is miscible with xylene but not with most alcohols or water); and (4) the cells in molten wax must then be manually organized and hardened on the underside of a tissue cassette so that a section of the wax block with the embedded tissue can be cut using a microtome.
U.S. Pat. No. 6,913,921 discloses methods and apparatuses for preparing embedded samples. The '921 patent, which is incorporated by reference as if set forth fully herein, discloses placing a biological sample on a filter, washing it with alcohol and xylene, and embedding the sample in paraffin wax. A drawback of the disclosed method is the use of a bulk paraffin reservoir, which requires special heating and pumping systems.